(1) Field of the Invention
The invention relates to an electrostatic precipitator with a number of collecting electrodes which are arranged in rows adjacent to each other and in respective pairs at equal distances from a respective discharge electrode (for instance wire) with which they are opposite.
(2) The prior art
Electrostatic precipitators are commonly used to precipitate dust from waste gas or expelled air from a dust producing plant such as mixing and grinding plant, sintering plant, power station etc. In order to be able to fulfil the requirements of anti-air pollution legislation, which have been made more and more stringent in the last two decades, it has become necessary to construct substantially larger electrostatic precipitators with collecting or precipitator electrodes each having a length of up to 14 meters. This length gives rise to various problems.
On the one hand, long precipitator electrodes must have sufficient mechanical strength and resistance to twisting; they are therefore usually provided with longitudinal corrugations and are crimped at their edges. They are mounted in a suspended array in the precipitator, being arranged in rows and connected at their upper and lower ends such as, for example, by a yoke or retainer made of two pieces of flat iron.
On the other hand, it is necessary to assure that the sheet metal precipitator electrodes can oscillate at their resonance frequency so that they can be rid of adhering dust by being subjected to rapping. The thickness of the sheet metal therefore should not exceed approximately 2.5 mm in order to ensure a sufficiently large amplitude of oscillation following an impact of a hammer weight which is appropriate for performing the dust-dislodging operation.
In previously proposed electrostatic precipitators, the precipitator electrodes have a relatively low mechanical strength: they have a substantial length and a low sheet metal thickness. In consequence, low frequency transverse and twisting oscillations occur in the precipitator electrodes, which are caused by the gas current flowing through the arrangement and can reach resonance levels. (In this respect, however, the resonance occurs at a very much lower frequency than the above mentioned resonance due to rapping). The consequence of this is that, owing to the reduction in the distances between the discharge electrodes and the precipitator electrodes, the amount of sparking increases and, as a result, the operational voltage is automatically reduced, which brings about a reduction in the precipitation output.
Attempts have already been made to provide a yoke-like retainer-like stiffening member halfway along the length of long precipitator electrodes in order to avoid the low frequency transverse and torsional oscillations. Furthermore, attempts have been made to arrange screw means and holding iron elements halfway along the length or to provide holding guide cords.
The disadvantage of these known solutions is that they, on the one hand promote local sparking that results in reduction in the operating voltage while, on the other hand substantial frictional wear occurs in contact zones under the action of the solid particles to be precipitated and the movement of the precipitator electrodes following the rapping. As a result, the discharge electrodes are damaged at certain regions by spark erosion and, furthermore, the thin precipitator electrodes are abraded and fractured. The frictional wear of the precipitator electrodes is furthermore augmented by spark erosion when the potentials are different. The efficiency and service life of the electrostatic precipitator are reduced as a result.